The war on the plastic bag has been waged across Canada and Europe, but a new study out of Scotland highlights how the issue is another prime example of the law of unintended consequences. This week, Britain’s pre-eminent food scientist, Hugh Pennington, emeritus professor of bacteriology at Aberdeen University, warned that using reusable bags could result in “an increase in the number of cases of food poisoning.” A bag that has carried meat, wrapped or unwrapped, “shouldn’t be used again” because it can harbour dangerous bugs, he said. It is not the first time that policy decisions have had unintended consequences.

The Daily Telegraph has another example of unintended consequences, in this case, the increase in cases of rickets in children:

Most people associate rickets with Victorian urchins. Over the past half a century, the disease was virtually wiped out. But, because of a series of social and cultural shifts, it is making a comeback, with a five-fold rise in cases in the past 15 years in the U.K.

Last week, the chief medical officer for England, Dame Sally Davies, said every child should be given vitamins in order to tackle rickets. The idea was welcomed by the medical establishment, which perhaps thought that it had seen the last of the characteristic “bowing” legs associated with the condition, as the bones buckle under the weight of the upper body.

Historically, the main cause of this was malnutrition. Rickets is, simply, a softening of the bones caused by a deficiency in vitamin D, calcium or phosphorus. All of these substances are needed in order to make bone, and when one or all are deficient, the bone cannot harden properly.

But the cases being seen today are almost entirely the result of a vitamin D deficiency due to a lack of sunlight: most of our vitamin D is made in our skin following sun exposure. For this reason, rickets was particularly prevalent in inner cities after the industrial revolution, because the smog and smoke that filled the air limited the amount of sun reaching people.

The current resurgence cannot be blamed on pollution. Public health campaigns have raised the issue of sunburn in children and the associated risk of skin cancer, meaning that children are now often covered up or slathered in sun block — so preventing sunlight from reacting with their skin to form vitamin D.

At the same time, children are increasingly sedentary and spend more time inside the house, watching TV and playing computer games. Parents are also more anxious about their children going out to play, fearful that they might be abducted by pedophiles. Wrapping our children in cotton wool has an unintended effect: once again, sunlight is not reaching their skin.

Australia has had its fair-share of animal-based unintended consequences. Here’s the tale of the cane toad by Tina Butler of mongabay (environmental science and conservation news site):

Before 1935, Australia did not have any toad species of its own. What the country did have however, was a major beetle problem. Two species of beetles in particular, French’s Cane Beetle and the Greyback Cane Beetle, were in the process of decimating the northeastern state of Queensland’s sugar cane crops. The beetle’s larvae were eating the roots of the sugar cane and stunting, if not killing, the plants. The anticipated solution to this quickly escalating problem came in the form of the cane toad. After first hearing about the amphibians in 1933 at a conference in the Caribbean, growers successfully lobbied to have the cane toads imported to battle and hopefully destroy the beetles and save the crops.

In early 1935, a box containing 102 toads from Hawaii — one place that had already brought in the amphibians for a similar purpose — arrived in Gordonvale, a small town just south of Cairns. After a short time in captivity, the population had multiplied to reach 3000, and in July of 1935, the cane toads were released into the fields. Initially, some naturalists and scientists warned of the risks in loosing the toads and protested. After a brief moratorium, the releases resumed in 1936. Australians, know the rest all too well.

The plan backfired completely and absolutely. As it turns out, cane toads cannot jump very high, only about two feet actually , so they did not eat the beetles that for the most part lived in the upper stalks of cane plants. Instead of going after the beetles, as growers had planned, the cane toads began going after everything else in sight–insects, bird’s eggs and even native frogs. And because the toads are poisonous, they began to kill would-be predators. The toll on native species has been immense.

Invasive species, as a general rule, live up to their name as non-native plants, animals, fungi and even pathogens that find their way to new territory and typically have a special affinity/predilection for wiping out the original inhabitants. They are a major problem around the globe, arriving in new ecosystems and wreaking environmental havoc and often economic damage in their new homes. The World Conservation Union (WCU) lists the world’s 100 worst of these destructive pests and cane toads have the dubious honor of being the unofficial poster child for the list and one of only three amphibians held in this unesteemed company.